“But man, unlike animals, is unique and depraved; and it all stems from Adam.”
I take it you doubt that animal nature might have been twisted by man’s sin?
Hmmmm...that's a good question that, quite frankly, I've never thought about. Are animals' nature twisted because of their surroundings, are their nature twisted because of the will of God (such as the "fear of man" falling on them after Noah), is it a combination, or none? I'm not sure.
The Christian position has been that everything is tainted but what does that mean for animals? In the OT if an animal such as an ox, had a history of gorging a person, it was considered sin on the animal and the ox was to be put to death. But I'm not sure that isn't too literal of an interpretation. All I can say, without more research, is that animals are not quite what they use to be and should be.